1. Field of the Invention
The present invention relates in general to a cutting tool, and more particularly to such a cutting tool including a cutter head and a holder that are detachably attached to each other.
2. Discussion of the Related Art
There are known cutting tools each of which is to be used for cutting a workpiece in an operation performed by a machine tool such as a machining center. In recent years, many of such cutting tools are formed of cemented carbide, for the purpose of increasing its machining efficiency and tool life. However, since the cemented carbide is a material expensive and hard to be machined, there is a problem that a product cost of an entirety of the cutting tool is inevitably increased due to increases in material and machining costs, particularly, where the cutting tool is of a so-called solid type in which a main body and a shank (holder) are provided by a single piece that is formed of the cemented carbide.
In view of this, there is proposed a cutting tool including a cutter head as the main body and a holder to which the cutter head is detachably attached. In the proposed cutting tool, the cutter head is formed of cemented carbide while the holder is formed of other material, so that the increase in the product cost of the entirety of the cutting tool can be restrained. In such a cutting tool, the cutter head is attached to the holder as described below.
JP-H07-171702A (publication of unexamined Japanese Patent Application laid open in 1995) discloses a cutting tool in which a cutting insert as the cutter head is fixed to the holder. Specifically described, the cutting insert is fitted at its supported portion in a recess that is formed in a distal end portion of the holder, and a screw fastener is provided to pass through a through-hole formed through the supported portion of the cutting insert and be tightly screwed into an internally threaded hole formed in a bottom of the recess of the distal end portion of the holder. That is, the cutting insert can be firmly fixed to the distal end portion of the holder owing to thread engagement established by the screw fastener. In this arrangement in which the cutting insert is detachably attached to the holder only by the thread engagement, the cutting insert can be easily replaced with a new one, for example, when the cutting insert is worn out.
JP-2002-103130A (publication of unexamined Japanese Patent Application laid open in 2002) discloses a cutting tool in which the cutter head is attached to the holder by thread engagement. Specifically described, the cutter head has a protrusion formed in its axial end portion, while the holder has a recess formed in its axial end portion. The protrusion of the cutter head has an external thread formed in its outer surface, and the recess has an internal thread formed in its inner surface, so that the cutter head is tightly screwed into the holder. That is, the cutter head can be firmly fixed at its protrusion in the recess of the holder owing to the thread engagement. In this arrangement in which the cutter head is detachably attached to the holder by the thread engagement, the cutter head can be easily changed to a new one, as needed, without changing the holder.
JP-2001-505136A (publication of unexamined Japanese Patent Application laid open in 2001) discloses a cutting tool in which the cutter head and a shank as the holder are attached to each other through a retainer interposed therebetween. Specifically described, the cutter head and the retainer have respective hook-shaped engaging portions, so that the cutter head is held in engagement at its engaging portion with the engaging portion of the retainer that is fitted in a hole of the shank. Thus, the cutter head is firmly fixed relative to the shank. In this arrangement, too, the cutter head can be changed to a new one, as needed, without changing the shank.
JP-2000-176723A (publication of unexamined Japanese Patent Application laid open in 2000) discloses a cutting tool in which the cutter head is attached to a shank as the holder, by means of shrinkage fitting. Specifically described, the cutter head has an axial protrusion while the shank has a recess or hole, such that the axial protrusion of the cutter head can be fitted into the hole of the shank, with the shank being heated. The cutter head is firmly fixed to the shank, since the diameter of the hole of the shank is reduced when the temperature of the shank is eventually returned to an ordinary temperature causing the shank to shrink. In this arrangement, the cutter head can be replaced with a new one, as needed, by heating the shank.
However, in each of the cutting tools disclosed in JP-H07-171702A and JP-2002-103130A in which the cutter head is attached to the holder by the thread engagement, external and internal threads could be damaged due to a cutting resistance exerted to the threads. Thus, the cutting tool is likely to suffer a problem that the firm fixation of the cutter head to the holder could be easily lost.
Further, in the cutting tool disclosed in JP-2001-505136A in which the retainer has to be interposed between the cutter head and the shank, the number of components of the cutting tool is increased whereby cost required for the components is problematically increased.
Further, in JP-2000-176723A, since the shank has to be heated each time the cutter head is attached to or removed from the shank, the cutting tool requires a heating device used to heat the shank, leading to the consequent increase in installation cost.